Methods are known in the prior art concerning copper hydrometallurgy which involve recovery of cuprous chloride from process solutions with subsequent reduction to produce and recover copper metal. Patents of this type include U.S. Pat. Nos. 3,798,026, 3,972,711, 4,039,324 and 4,013,457. Major work in this field may be found in U.S. Pat. Nos. 3,785,944 and 3,879,272 to Atwood et al., which are concerned with hydrometallurgical processes for pollution-free recovery of metallic copper from copper ores, such as chalcopyrite, the most common copper-containing ore in the United States. U.S. Pat. No. 3,785,944 describes a basic hydrometallurgical process for processing copper sulfide ore concentrates, especially those containing chalcopyrite. This process has four basic stages: an oxidation stage in which copper-containing materials are oxidized with a solution containing ferric chloride and cupric chloride to form a solution containing ferrous chloride and cuprous chloride; a reduction stage in which any remaining cupric chloride in the solution from the oxidation stage is reduced to cuprous chloride, preferably by use of fresh cement copper; a copper recovery stage in which metallic copper is recovered from the cuprous chloride solution, preferably by electrolysis; and a regeneration purge stage in which ferric chloride and cupric chloride are regenerated by oxidation with concurrent purge of excess iron as well as sulfate ions and other impurtiies. The resulting leach solution is then used to oxidize additional copper-containing ore.
U.S. Pat. No. 3,879,272 to the same inventors describe improvements on the process of U.S. Pat. No. 3,785,944, especically in combining the oxidation and regeneration-purge stage and use of KCl in the system. In these patents, the reduced leach solution or electrolyte which is subsequently electrolyzed, contains impurities which are electrolyzed with the copper and it is desirable that these impurities be removed prior to electrolysis.
U.S. Pat. No. 3,972,711 claims an improvement over the Atwood patents on the basis that because the reduced leach solution of Atwood contains certain impurities, improved results are obtained by crystallizing cuprous chloride from the system so as to produce a purer grade of copper. In this process, the cuprous chloride is crystallized in the presence of a specified amount of cupric chloride.
In the system described in U.S. Pat. Nos. 3,785,944 and 3,879,272, there results, from the reaction of chalcopyrite with cupric chloride in the presence of potassium chloride, at least a 50% decomposition of the chalcopyrite. From this reaction, there is recovered a solution which contains cuprous chloride and potassium chloride.
In copending Application, Serial No. (Case 070-023) filed of even date herewith by Leonard R. Ochs, there is disclosed a method by which the hydrometallurgical processes described in U.S. Pat. Nos. 3,785,944 and 3,879,272 can be carried out with improvements in obtaining aa purer grade of copper by minimizing the presence of impurities within the system prior to hydrolysis. This improvement provides a crystallization stage wherein solids in the form of complex salts of potassium chloride and cuprous chloride are crystallized and removed from the system to provide a resultant increase in the copper product produced. These complex salts of potassium chloride and cuprous chloride, of the formula K.sub.2 CuCl.sub.3 or 2KCl.CuCl, may then be removed from the system and used as desired. Some silver in the system may also be precipitated with these salts.
The present invention provides a method whereby these complex or double salts of cuprous chloride and potassium chloride can be treated so as to recover the individual salts, cuprous chloride and potassium chloride, and also recover any silver, which may be present in the double salt mixture.
To the present time, there have not been efficient and economic procedures by which these complex salts can be processed so as to recover the individual components, cuprous chloride and potassium chloride. For example, if it were desired to isolate solid potassium chloride from a solution of these salts, a large amount of water would have to be evaporated to concentrate the solution.
Complex salts of potassium chloride and copper chloride are also known in the art and have been reported in the literature by several authors. Species such as KCuCl.sub.2, K.sub.2 CuCl.sub.3 and KCuCl.sub.2.H.sub.2 O are reported by the following authors: J.J.P. Valeton and W. Fromel, Z. anorg. allgem. Chemie, 137, 91 (1924); O.A. Chaltykyan, Zhur. Obshchei Khim., 18, 1626 (1948); W.U. Malik, et al., Z. anorg. allgem. Chemie, 299, 322 (1959). However, none of these complexes are recovered and produced by crystallization from process streams of any type.
The prior art, as suggested in certain U.S. patents, recognizes that cuprous chloride may be crystallized from a solution as a double salt or complex with ammonia, as shown for example, in U.S. Pat. No. 1,814,822. Further, U.S. Pat. No. 3,278,232 disclosesthat cupric ion combines with ammonia in aqueous solution. Also, U.S. Pat. No. 3,279,897 teaches that ammoniation of water soluble compositions containing both sodium chloride and potassium chloride causes potassium chloride to be precipitated from solution when working with systems, such as NaCl-KCl-NH.sub.3 -H.sub.2 O. Further, U.S. Pat. No. 3,501,266 suggests that potassium halide salts may be precipitated from aqueous solutions of potassium halide salts by addition of ammonia to selectively precipitate the potassium halide salts.
It is also known from U.S. Pat. No. 3,502,431 to carry out the reaction of ammonium chloride with a reaction mass which may include metallic copper, potassium chloride and alumina. Further, Russian Pat. No. 430,566 deals with complexes of cuprous chloride and ammonium chloride in aqueous solutions.
In none of this prior art, however, is there any suggestion for the decomposition of complex salts of potassium chloride and cuprous chloride to recover the valuable components contained therein in an economically feasible manner. The present invention provides a method of this type.